Project 5

Molecular basis of the aberrant signaling behavior of Ras-related proteins that lead
to cancer

(Paul Adams)

A major challenge still facing the biomedical community is the limited development
of therapeutic strategies to tackle the oncogenic potential of the Ras super-family
of proteins. Strategies that will have high impact on future drug design must target
new molecular features of cell signaling proteins involved in cell proliferation and
transformation, as well as other oncogenic events. The activity of Ras-related proteins,
is dictated by its nucleotide-bound state (GTP-bound active; GDP-bound form inactive).
These states can be distinguished by conformational differences, most of which are
localized in two relatively flexible “Switch” regions as characterized by internal
dynamics on multiple timescales, and this flexibility may be essential for protein
interactions, some of which can lead to abnormal cell-signaling activity involving
Ras-related proteins.

Our long-term research goals are to understand the molecular basis of the aberrant
signaling behavior of Ras-related proteins that lead to cancer, facilitating approaches
to the identification and development of potential targets for therapeutic design.
Presently, we are using molecular biology, as well as, biophysical and biochemical
techniques in the design of strategies to study molecular details of the Ras proteins
Cdc42 and Rheb that we expect to aid our understanding of how changes in conformation/dynamics
of these proteins and interaction with regulator/effectors proteins affect various
important Ras-regulated signal transduction pathways.

Recently, studies from our laboratory on the biomolecular dynamics, structure, and
biological function of a mutant of Cdc42, relative to wild type protein highlighted
that, in addition to strategies to block Ras-protein interactions, strategies to restrict
the conformational flexibility of important binding regions of Ras leading to the
inhibition of effector interactions that facilitate aberrant signaling activity may
also have therapeutic potential (Chandreshekar, et al., 2011, Biochemistry, 50, p.
6196-207).

With a better understanding of conformational changes in Ras proteins that affect
normal cell-signaling, we expect to provide information at the molecular level that
will shed light on mechanisms of specific signal transduction pathways regulating
oncogenic events.

Structure of Cdc42(T35A)-GDP, a single-point mutant construct of the Ras protein Cdc42
in a region known to be important in effector protein interactions.

(A) Stereoview of the backbone ensemble of the Switch I region of wild-type Cdc42
and Cdc42(T35A). (B) Backbone of the Switch I region colored on the basis of best-fit
dynamics model assignments from dynamics calculations. From reference (1).

2D 15N-HSQC of Cdc42 wildtype (black) overlaid with Cdc42T35A (red). The inset (upper right
corner of figure) highlights a region of the spectrum containing resonances from three
residues on the C-terminal portion of the Switch 1 region of Cdc42T35A (Residues 38,
40 and 41) not detected in the HSQC spectrum of Cdc42 wild type. from reference (1)